What tables will lean a car out?

[Stangkiller]

I'm working on getting my car at least driveable before doing the auto-tune with the VE table. My car is always pig rich, and i'm running a very low VE table. <low compared to other tunes of similarly modded cars>.

What other tables will affect my fuel trims? On my last drive, the car threw two codes, both saying Fuel Trim too Rich. After i threw the codes the car drove much better.

Anyhelp would be greatly appreciated!

:cheers:

[SSpdDmon]

Since you still have fuel trims coming on, you're in closed loop and commanding a stoich (14.63) AFR. In closed loop, the car tries to maintain that using the O2 sensors in the exhaust. The two main tables in closed loop used for fueling are the MAF and VE. If the MAF is still hooked up, that's where the extra fuel is coming from. Either turn your MAF off, tune your VE in speed density first and re-enable the MAF for recalibration....or....put the VE back to stock, leave the MAF stock, and tune with the injector tables.

[Stangkiller]

Thank you for the info.

Sounds to me like you're saying my MAF table is wrong.

My understanding is the maf flows what it flows, and is not really a tuning tool. I should have the correct table for my maf, and that should be it as far as correcting the maf goes?

Thanks!
Chris

[SSpdDmon]

There are two main theories to tuning that I see on the net. One is what people consider "old-school" and the other is what many try to do. Personally, I think the old school way works best for forced induction cars and it's how most of the pro's tune (ie Lingenfelter). Basically, they leave the VE and MAF tables alone. Then, based on the AFR read in the exhaust with a WBO2, they decrease/increase the injector flow rate table to richen/lean the fueling delivered at various levels of manifold vacuum. WOT fueling is then dialed in with the PE table.

Many people online consider this old-school way of tuning "jenkity" because you're in essence tricking the PCM into thinking the injectors are bigger or smaller than they really are. Therefore, the PCM alters the amount of time they stay open to fuel the motor. You're also depending heavily on the MAF sensor. In the (rare) case that it fails, your car isn't going anywhere.

Tuning the other way, people disable their MAF and reverse engineer thier VE table in speed density by observing commanded vs actual AFR's. The benefit of this is - incase of a MAF failure, you can still drive the vehicle without concern for the motor's safety & some argue better transitional throttle fueling. The problem is, it can be a time consuming effort trying to dial it in with variations in conditions from day to day. Once the VE table is dialed in, the MAF is re-enabled and reverse engineered in the same manner. However, some end up increasing the values in the MAF on modified cars so much sometimes that it eats up the limits, or range, in the MAF table (PCM can only account for 512 grams/sec). Next thing you know, your MAF peaks out at 10,750Hz instead of 11,250Hz like it used to (stock '02 f-body MAF table referenced).

The second method seems to use the PCM's OS the way it was theoretically designed to work. However, the hardware limitations sometimes make it difficult to tune with. If you have the time, patience and can get it to work, more power to you. But, you won't be able to dial in part throttle and WOT tuning in 1 days time using that method.

[Stangkiller]

Thank you very much. My goal is to learn the second tuning method, and actually get the car tuned properly.

Right now, i'm still trying to get acquainted with EFI-Live, and many of the tuning theory's as well as just trying to make my car driveable.

I did upgrade my car to the custom OS 3, after adding LQ-9 heads. Today i finally got the car to idle <adding more timing at idle.> But it's still way rich. Thanks for the info, i'm going to try another MAF table, to see if i can't lean it out a bit more.

[joecar]

Hi Chris,

have you seen the AutoVE tutorial...?

http://www.efilive.com/download.aspx#downloads7

Also, if you're running too rich, are you sure you have no air leaks...?

Cheers,
Joe

[Stangkiller]

Hi Chris,

have you seen the AutoVE tutorial...?

http://www.efilive.com/download.aspx#downloads7

Also, if you're running too rich, are you sure you have no air leaks...?

Cheers,
Joe
I've got the car back to driveable now.

I plan on running the Auto VE shortly. I just got the adaptor for my wideband this weekend. So i'll be doing the auto-tune sometime soon.

I took a look at my MAF table, i have no clue where it came from or how i accidentally adjusted it. But it was WAY off. I had a stock 02 z06 tune, so I copied that MAF over. The car runs MUCH better. Still rich....But it sounds like i've got a pretty bad exhaust leak, <infront of my O2 sensors> My new exhaust gaskets will be here on Friday.

When you say Air leaks. You're suggesting maybe my Manifold is leaking? I did just swap heads, so i can't rule that out.

[joecar]

Air leak = any leak that introduces air (unaccounted for by MAF and/or VE table) that causes PCM to add more fuel.

That can be exhaust and/or intake air leaks (because both would cause the O2S to read lean, which would cause the PCM to add fuel, showing up as very postive LTFT's; exhaust leak would cause O2S to read lean due to added oxygen after combustion; intake leak would cause lean combustion; both cases O2S cause PCM to compensate and add fuel).

So it would be good idea to check from MAF all the way to the O2S, just in case (including PCV plumbing).

[TAQuickness]

Thank you for the info.

Sounds to me like you're saying my MAF table is wrong.

My understanding is the maf flows what it flows, and is not really a tuning tool. I should have the correct table for my maf, and that should be it as far as correcting the maf goes?

Thanks!
Chris


Yes and no. Mass air flow is Mass airflow. But keep in mind that the PCM never measures air (mass) flow. All air flow values are calculated or in table form.

[joecar]

Also, the MAF may be sensitive to any changes upsteam (lid, filter, plumbing) and/or downstream (cam reversion, pulse harmonics, intake, heads).

[Stangkiller]

Air leak = any leak that introduces air (unaccounted for by MAF and/or VE table) that causes PCM to add more fuel.

That can be exhaust and/or intake air leaks (because both would cause the O2S to read lean, which would cause the PCM to add fuel, showing up as very postive LTFT's; exhaust leak would cause O2S to read lean due to added oxygen after combustion; intake leak would cause lean combustion; both cases O2S cause PCM to compensate and add fuel).

So it would be good idea to check from MAF all the way to the O2S, just in case (including PCV plumbing).
Thank you for all this help guys!

My LTFT's are both negative on both sides...however it's less negative on my #2 sensor...i'm guessing thats caused by the exhaust leak.


I extended my O2 sensors. Is there any way that 2' extension may affect my reading, or is there a way to compensate?

[Stangkiller]

Also, the MAF may be sensitive to any changes upsteam (lid, filter, plumbing) and/or downstream (cam reversion, pulse harmonics, intake, heads).
When you say sensitive to these changes. What do you mean? Meaning the reading may be affected due to environmental changes? Thus the table, may be affected?

I can't wait to cut this MAF. It'll be a few more days though.

[TAQuickness]

When you say sensitive to these changes. What do you mean? Meaning the reading may be affected due to environmental changes? Thus the table, may be affected?

I can't wait to cut this MAF. It'll be a few more days though.

It has more to do with how a mass flow meter works. A properly installed mass flow meter will have a length of straight pipe = to 5 times the diameter of the orifice upstream of the metering elements (I don't recall the down stream length atm).

For obvious reasons, you can't do this in a vehicle. GM implements screens and air foils to straighten the air flow across the sensor elements to compensate for the poor installation conditions.

In any case (vehicle installation), the measured air flow from the MAF is not accurate - BUT - it's consistent so long as you don't change the upstream or downstream characteristics of the air flow. Because the MAF is consistent, it's output can be used to look up an air flow value that is more accurate.

Lot's more info here:
http://www.ls1tech.com/forums/showthread.php?t=363392

[Stangkiller]

Hmm, awesome! Thanks!

[joecar]

Thank you for all this help guys!

My LTFT's are both negative on both sides...however it's less negative on my #2 sensor...i'm guessing thats caused by the exhaust leak.


I extended my O2 sensors. Is there any way that 2' extension may affect my reading, or is there a way to compensate?
You can take those 2' extensions and with a DMM ohm them out...
If they show less than 0.2 ohms, they should have negligble effect;
If they have the terminals crimped on properly and the wires are not stretched/broken then this will be the case.

[Stangkiller]

You can take those 2' extensions and with a DMM ohm them out...
If they show less than 0.2 ohms, they should have negligble effect;
If they have the terminals crimped on properly and the wires are not stretched/broken then this will be the case.
Awesome, thank you. I soldered in the extension using teflon/silver based wire. I'll go buy better wire, if there really is any resistance...But, i think this was some of the best wire for the job.

:cheers:

[TAQuickness]

Hmm, awesome! Thanks!

No problem.

BTW - Welcome to the forum

[Stangkiller]

No problem.

BTW - Welcome to the forum
Thank you, i'm really enjoying this forum. And have a feeling i'll be posting quite a bit more over the next few weeks as i start the tuning process on my car.

:cheers:
Chris